There are two reasons for vertical stripes on TV picture.
First – incorrect setting of BIOS PCI Latency Timer. In this case the stripes are looked as green or magenta and covering 4/5 of picture surface. Stripes are removed by selection of PCI Latency of DMA controller directly in "Video" settings of Behold TV application.
Second reason of appearing stripes – noise pickup, caused by PCI bus work during data packets transmission. The noise is picked up immediately on RF-input of tuner and neither depends on power supply quality nor on any BIOS settings of motherboard. Mainly it depends on tuner placement, PC case screening capability, motherboard schematics, antenna cable quality and it's placement in immediate proximity to PC case. This noise become noticeable in low frequency band (49-200 MHz) when signal level is weakened by 15-20 dB in comparison with normal level. You may never see such noise in TV sets because TV set has no the source of the noise – PCI bus. The only correct and reliable way to overcome this effect – to rise TV signal strength to normal level. For this you can do the following:
1) Ensure that all contacts are reliable, well connected and matched along the whole TV cabling.
2) Minimize the number of cable splitting. Each cable splitter divides the signal power between all signal consumers. Use only high quality splitters.
3) Use only high quality TV cable. Cable must have impedance 75 Ohms and must not be too thin (RG-59 standard compliance). Cable should have double screening - wire net and twisted foil. Do not connect two or more pieces of cable together, – each connection will result in signal loss and reflexion. Provide minimum of cable interconnections.
4) Use only all-metal connectors. Avoide using connectors in plastic case.
5) Place ferrite bead filter to the cable in the vicinity of tuner input. This filter supresses the main – cophasal component of noise, but the suppression is often insufficient and mainly in low frequencies range. You may buy such filter in radio component store.
6) If nothing else helps, use RF signal amplifier. Do not place amplifier near the PC case or other electronic devices.
To determine reason of noise more precisely try to apply video signal to video inputs of tuner from external source, for example from VCR. If the noise persists, the reason is incorrect PCI Latency Timer value. If disappeared – problem in weak TV-signal.